Answer:
You have a New Model Single Six which appears to have been manufactured in 1977. For a more detailed product history, you can write to Ruger Customer Service at:
Sturm, Ruger & Co., Inc.
Records Department
411 Sunapee Street
Newport, NH 03773
or you can fax a request to:
603-863-9371
or you can call at:
603-865-2424
They will need the model and serial number. If you call, you'll usually get their voicemail. Leave a detailed message with the above information, and they'll get back to you usually within a week.